Interleukin-11 acts synergistically with bone morphogenetic protein-2 to accelerate bone formation in a rat ectopic model.

We previously demonstrated that recombinant human interleukin-11 (rHuIL-11) induced osteoblast differentiation of C3H10T1/2 progenitor cells and also acted synergistically with recombinant human bone morphogenetic protein-2 (rHuBMP-2) in performing the same function. In this study, we investigated the effect of rHuIL-11 and rHuBMP-2 on bone formation in a rat ectopic model. When placed in rats, implants consisting of polymer-coated gelatin sponges containing various concentrations of rHuBMP-2 showed a dose-dependent increase in calcium content. This was confirmed by radiographic analysis of the implants. Although implants containing rHuIL-11 alone did not accumulate calcium, implants containing a combination of rHuBMP-2 and rHuIL-11 had significantly higher calcium levels than those containing rHuBMP-2 alone. This increase was rHuIL-11 dose dependent. The synergistic effect of 20 micrograms rHuIL-11 and 6 micrograms rHuBMP-2 on bone formation was estimated to be 1 week in advance of that of 6 micrograms rHuBMP-2 alone. Histologic examination revealed that the combination of rHuIL-11 and rHuBMP-2 caused spindle cells to accumulate around implants and induced cell infiltration into implants. Bone formation occurred faster in implants with the combination of rHuIL-11 and rHuBMP-2 compared with rHuBMP-2 alone. These results suggest that rHuIL-11 acts synergistically with rHuBMP-2 to more rapidly stimulate bone formation compared with rHuBMP-2 alone. This novel combined therapy may be of great clinical benefit in bone healing.     

Synergism between interleukin-11 and bone morphogenetic protein-2 in the healing of segmental bone defects in a rabbit model.

Recombinant human interleukin-11 (rHuIL-11) and recombinant human bone morphogenetic protein-2 (rHuBMP-2) have been shown to act synergistically in the induction of osteoblast differentiation. To determine whether these two proteins can be used clinically in fracture healing and reconstructive surgery, we investigated whether rHuIL-11 and rHuBMP-2 act synergistically to heal segmental bone defects in a rabbit model. A 1.5-cm segmental defect was created in the right ulnar diaphysis of 20 Japanese white rabbits. Polylactic-co-glycolic acid (PLGA)-coated gelatin sponges (PGS) permeated with rHuBMP-2 (n = 8), rHuIL-11 plus rHuBMP-2 (n = 8), or rHuIL-11 (n = 4) were implanted into the bone defects. Radiographs were scored by two independent observers for bone formation and union rates after 2, 3, 4, and 8 weeks. Bone formation was higher in rabbits implanted with rHuBMP-2 plus rHuIL-11 than in those implanted with rHuBMP-2 alone, reaching statistical significance after 4 weeks. At early time points, the union rate in rabbits implanted with rHuBMP-2 plus rHuIL-11 was higher than in rabbits implanted with rHuBMP-2. At 2, 4, and 8 weeks, new bone volume was significantly higher in rabbits administered rHuIL-11 plus rHuBMP-2 than in those given rHuBMP-2 alone. In contrast, mechanical testing after 8 weeks showed that bone strength in the two groups of rabbits was equivalent. These findings show that rHuIL-11 and rHuBMP-2 act synergistically to accelerate bone formation without affecting bone strength. Treatment with a combination of rHuIL-11 and rHuBMP-2 may thus be of great benefit in fracture healing and for patients undergoing reconstructive surgery.     

Tissue transglutaminase (TG2) activity regulates osteoblast differentiation and mineralization in the SAOS-2 cell line

Tissue transglutaminase (type II, TG2) has long been postulated to directly promote skeletal matrix calcification and play an important role in ossification. However, limited information is available on the expression, function and modulating mechanism of TG2 during osteoblast differentiation and mineralization. To address these issues, we cultured the well-established human osteosarcoma cell line SAOS-2 with osteo-inductive conditioned medium and set up three time points (culture days 4, 7, and 14) to represent different stages of SAOS-2 differentiation. Osteoblast markers, mineralization, as well as TG2 expression and activity, were then assayed in each stage. Furthermore, we inhibited TG activity with cystamine and then checked SAOS-2 differentiation and mineralization in each stage. The results showed that during the progression of osteoblast differentiation SAOS-2 cells presented significantly high levels of osteocalcin (OC) mRNA, bone morphogenetic protein-2 (BMP-2) and collagen I, significantly high alkaline phosphatase (ALP) activity, and the increased formation of calcified matrix. With the same tendency, TG2 expression and activity were up-regulated. Furthermore, inhibition of TG activity resulted in a significant decrease of OC, collagen I, and BMP-2 mRNA and of ALP activity and mineralization. This study demonstrated that TG2 is involved in osteoblast differentiation and may play a role in the initiation and regulation of the mineralization processes. Moreover, the modulating effects of TG2 on osteoblasts may be related to BMP-2.     

Interleukin-11 modulates Th1/Th2 cytokine production from activated CD4+ T cells.

Recombinant human interleukin-11 (rHuIL-11) is a pleiotropic cytokine with effects on multiple cell types. rHuIL-11 reduces activated macrophage activity and downregulates production of proinflammatory mediators, such as tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO). In vitro and in vivo, rHuIL-11 inhibits production of key immunostimulatory cytokines, including IL-12 and interferon-gamma (IFN-gamma). rHuIL-11 has recently demonstrated immunomodulatory activity to downregulate IFN-gamma production, increase IL-4 production, and reduce inflammatory tissue injury in a human psoriasis clinical trial. The cellular mechanisms of these effects are not fully elucidated. We demonstrate here that expression of gp130 and IL-11 receptor (IL-11R) alpha mRNA, components of the IL-11R complex, are detected in human and murine CD4(+) and CD8(+) lymphocytes, suggesting that rHuIL-11 can directly interact with T cells. In a cell culture model of murine T cell differentiation, rHuIL-11 acts to inhibit IL-2 production as well as IL-12-induced IFN-gamma production and enhances IL-4 and IL-10 production. rHuIL-11 had no effect on T cell proliferation. The ability of rHuIL-11 to modulate cytokine production from activated CD4(+) T cells provides a mechanism through which rHuIL-11 may ameliorate such inflammatory diseases as psoriasis.     

A Novel Semisynthetic Molecule Icaritin Stimulates Osteogenic Differentiation and Inhibits Adipogenesis of Mesenchymal Stem Cells

Background We previously reported that the constitutional flavonoid glycosides derived from herb Epimedium (EF, composed of seven flavonoid compounds with common nuclear stem) exerted beneficial effects on the bone, including promoting bone formation and inhibiting bone marrow fat deposition. Recent in vivo study showed that Icaritin was a common metabolite of these constitutional flavonoid glycosides, indicating that Icaritin is a bioactive compound. The present study was designed to investigate whether Icaritin could promote osteogenic differentiation and suppress adipogenic differentiation of marrow mesenchymal stem cells (MSCs).Methods Primary MSCs were harvested from adult mice and exposed to Icaritin to evaluate whether it could promote osteogenesis and suppress adipogenesis using the following assays: determination of alkaline phosphatase (ALP) activity and mineralization; mRNA expression of osteogenic differentiation marker Runx2; osteocalcin and bone sialoprotein (BSP) by RT-PCR; quantification of adipocyte-like cells by Oil Red O staining assay and mRNA expression for adipogenic differentiation markers peroxisome proliferator-activated receptor gamma (PPARγ); adipocyte fatty acid binding protein (aP2) and lipoprotein lipase (LPL) by RT-PCR. For the underlying mechanism, glycogen synthase kinase-3beta (GSK3β) and β-catenin were also explored by western blotting.Results Icaritin promoted osteogenic differentiation and maturation of MSCs as indicated by increased mRNA expression for Runx2, osteocalcin and BSP, and enhanced ALP activity and mineralization; Icaritin inhibited adipogenic differentiation, as indicated by decreased mRNA expression for PPARγ, LPL, aP2, and suppressed formation of adipocyte-like cells; Icaritin inactivated GSK3β and suppressed PPARγ expression when promoting osteogenesis and suppressing adipogenesis of MSCs.Conclusion This was the first study demonstrating that the novel semisynthetic molecule Icaritin could stimulate osteogenic differentiation and inhibit adipogenesis of MSCs, which was associated with the suppression of GSK3β and PPARγ.     

Differentiation of osteoblasts in three-dimensional culture in processed cancellous bone matrix: quantitative analysis of gene expression based on real-time reverse transcription-polymerase chain reaction

Processed bovine cancellous bone (PBCB) is an attractive material for tissue engineering of bone. It is biocompatible, osteoconductive, nonimmunogenic, and porous and its biomechanical properties are close to those of native bone. In this study, differentiation of primary rat osteoblasts (rOBs) incubated on PBCB was investigated in vitro. rOBs were isolated and expanded in two-dimensional culture. Expanded rOBs were seeded into PBCB disks and cultured either in basal medium (BM) or differentiation medium (DM) containing ascorbic acid, beta-glycerol phosphate, and dexamethasone. Alkaline phosphatase (ALP) activity and RNA expression of ALP, bone sialoprotein (BSP), collagen type I (COL1), osteocalcin (OC), and osteopontin (OPN) were assessed by chemiluminescence assay and quantitative real-time RT-PCR over 14 days. Histologic analysis was performed on day 14. ALP increased over the observation period independent of stimulation. OPN and BSP expression was significantly higher in the DM group whereas COL1 and OC expression was significantly higher in the BM group. Matrix calcification was detectable only in the DM group by von Kossa stain. The observed expression patterns suggest a physiological response of rOBs to the differentiation stimulus. PBCB is a suitable matrix for in vitro differentiation of osteoblasts. Cell-seeded PBCB is a potential osteogenic construct for in vivo application.     

Calcium phosphate-chitosan composite scaffolds for bone tissue engineering

Macroporous calcium phosphate-chitosan composite scaffolds were fabricated and evaluated for use in bone tissue engineering. Human osteoblast-like MG63 cells were cultured on the composite scaffolds, and their response to the materials was studied. Cell morphology, total protein content, and expression of classic markers for osteoblast differentiation were characterized. MG63 cells on the hydroxyapatite scaffolds nesting chitosan sponges (HC1) showed significantly higher alkaline phosphatase (ALP) level and osteocalcin (OC) production during the 11-day culture period, compared with the control culture on tissue culture plates. Cells on the chitosan scaffolds incorporated with hydroxyapatite powders (HC2) exhibited lower ALP activity during the 11-day culture period and OC secretion during the first 7 days, in comparison with that on HC1. The addition of calcium phosphate glass as in HC3 scaffolds increased the ALP and OC levels of MG63 cells. Our study indicated that the hydroxyapatite-matrix composite scaffolds might enhance the phenotype expression of MG63 cells, in comparison with chitosan-matrix scaffolds. Soluble calcium phosphate glasses should be added to the scaffolds to prevent chitosan from fast degradation that may affect the differentiation of osteoblast cells.     

Basic fibroblast growth factor enhances in vitro mineralization of rat bone marrow stromal cells grown on non-woven hyaluronic acid based polymer scaffold.

A biodegradable non-woven hyaluronic acid polymer scaffold (Hyaff 11) was analysed in vitro as a carrier vehicle for differentiation and mineralization of rat bone marrow stromal cells (BMSC). BMSC were grown on Hyaff 11 in a mineralizing medium in the presence/absence of basic fibroblast growth factor (bFGF). Osteoblastic differentiation was investigated by light and electron microscopy analysing the expression of osteogenic markers: calcium, alkaline phosphatase (AP), osteopontin (OP), bone sialoprotein (BSP) and collagen type 1. We also measured proliferation, AP activity and mRNA expression of AP and osteocalcin (OC). Electron microscopy and Toluidine-blue staining demonstrated that bFGF accelerated (day 20 vs. day 40) and increased mineralization. With bFGF, calcium, OP and BSP were strongly enhanced at day 40, whereas AP decreased. Our in vitro results demonstrate that Hyaff 11 is a useful vehicle for growth, differentiation and mineralization of rat BMSC, and that it permits bone development.     

Glucocorticoid‐induced differentiation of primary cultured bone marrow mesenchymal cells into adipocytes is antagonized by exogenous Runx2

Lin L, Dai S‐Dong, Fan G‐Yu. Glucocorticoid‐induced differentiation of primary cultured bone marrow mesenchymal cells into adipocytes is antagonized by exogenous Runx2. APMIS 2010; 118: 595–605. Long‐term clinical use of glucocorticoids often causes the serious side effect of non‐traumatic avascular osteonecrosis. The aim of this study was to examine the effects and mechanisms of a glucocorticoid, dexamethasone (Dex), on differentiation of primary cultured rat bone marrow mesenchymal cells (BMCs). We also tried to block the inhibitory effects of Dex on osteoblast differentiation. Adipocyte markers (peroxisome proliferator‐activated receptorγ‐2 and aP2) were increased in response to Dex treatment in a dose‐ and time‐dependent manner, while osteoblastic markers [Runx2, COL 1, osterix, alkaline phosphatase (ALP) and OC] were down‐regulated, consistent with ALP and osteocalcin promoter activity. To validate the effects of Runx2 on the expression of osteogenesis and adipocyte genes, pCMV/Flag‐Runx2 was transfected into BMCs, and relevant markers were detected after 10^?7 M Dex treatment for 48 h. The results indicated that Dex treatment induced adipogenic differentiation and suppressed proliferation. No significant difference was detected in expressions of these genes between Runx2‐transfected cells and Dex‐treated BMCs. These data suggest that Dex primarily induced adipocyte differentiation of BMCs. Exogenous Runx2 can antagonize the effect of Dex on osteoblast differentiation.     

ERK信号通路在檞皮素促大鼠MSCs成骨分化中的作用

目的:观察细胞外信号调节激酶(ERK)信号通路在檞皮素(QUE)促进SD大鼠骨髓间充质干细胞(MSCs)成骨分化过程中的作用。方法:(1)用0.01μmol/L、0.1μmol/L、1μmol/L、10μmol/L和100μmol/LQUE干预MSCs,MTT法检测各浓度QUE对MSCs增殖的影响,碱性磷酸酶(ALP)测定试剂盒检测各浓度QUE对MSCsALP表达的影响;(2)用ERK1/2抑制剂干预后,加入QUE,用ALP测定试剂盒检测ALP的表达,ELISA法检测Ⅰ型胶原(ColⅠ)和骨钙素(BGP)的表达,Westernblotting检测ERK1/2的表达,荧光定量PCR检测转化生长因子β₁(TGF-β₁)mRNA、骨形成蛋白2(BMP-2)mRNA和核心结合因子α1(Cbfα1)mRNA表达。结果:(1)0.1μmol/L、1μmol/L和10μmol/LQUE剂量依赖性地促进MSCsALP的表达,同时能促进MSCs的增殖;(2)与空白组相比,QUE组ALP、BGP和ColⅠ表达均增加(P<0.01),加入ERK1/2抑制剂后,磷酸化的ERK1/2表达减少(P<0.05),同时ALP、BGP和ColⅠ表达降低(P<0.01);(3)与空白组比较,QUE组TGF-β₁mRNA、BMP-2mRNA和Cbfα1mRNA的表达均增加(P<0.05),加入ERK1/2抑制剂后这3个基因的表达都下降(P<0.05)。结论:一定浓度的QUE能促进MSCs的增殖和成骨分化,ERK通路的激活在此过程中起到了重要的作用。     

木通皂苷D通过丝裂原活化蛋白激酶信号通路促进大鼠骨髓间充质干细胞分化为成骨细胞

目的:探讨木通皂苷D(ASD)是否促进大鼠骨髓间充质干细胞(BMSCs)分化为成骨细胞及其机制。方法:分离培养大鼠BMSCs;观察ASD对其向成骨细胞分化的影响以及p38丝裂原激活蛋白激酶(p38MAPK)抑制剂SB203580和细胞外信号调节激酶(ERK)抑制剂PD098059的干预作用;检测BMSCs分化过程中碱性磷酸酶(ALP)活性和骨钙素(OC)含量;实时荧光定量PCR检测护骨素(OPG)和核因子κB受体活化因子配体(RANKL)mRNA的表达;Westernblotting法检测p38MAPK和ERK活性水平。结果:ASD处理后第9d,成骨性分化标志物OPGmRNA表达量明显增高,RANKLmRNA的表达量明显降低,同时显著提高BMSCs分化为成骨细胞的ALP活性和OC的表达,而且p38MAPK和ERK活性也显著增加。SB203580和PD098059则显著抑制ASD的成骨作用。结论:ASD在体外具有促进大鼠BMSCs向成骨细胞分化的作用,这一作用与MAPK途径的p38MAPK和ERK蛋白有关。     

Osteogenic response of mesenchymal stem cells to continuous mechanical strain is dependent on ERK1/2-Runx2 signaling

Mechanical stimuli are responsible for bone remodeling during orthodontic tooth movement. The role of mechanical stimulation in the regulation of the fate of bone mesenchymal stem cells (BMSCs) is of interest in bone regeneration and tissue engineering applications. However, the signaling pathway involved in strain-induced biochemical events in BMSCs is not well established and can be controversial. This study investigated strain-induced proliferation and differentiation of BMSCs, as well as the mechanism of mechanotransduction. BMSCs were exposed to continuous mechanical strain (CMS) of 10% at 1 Hz. The results showed that CMS reduced the proliferation of BMSCs and stimulated osteogenic differentiation by activating Runx2, followed by increased alkaline phosphatase (ALP) activity and mRNA expression of osteogenesis-related genes (ALP, collagen type I and osteocalcin). Furthermore, the phosphorylation level of extracellular regulated protein kinase (ERK)1/2 increased significantly at the onset of strain. However, the presence of U0126, a selective inhibitor of ERK1/2, blocked the induction of Runx2 and subsequent osteogenic events. These findings demonstrate that CMS regulated Runx2 activation and favored osteoblast differentiation through activation of the ERK1/2 signaling pathway. These results will contribute to a better understanding of strain-induced bone remodeling and will form the basis for the correct choice of applied force in orthodontic treatment.     

梓醇对OB-OC共育体系中OB、OC活性及OBERα、βmRNA表达的影响

目的:观察中药单体梓醇在成骨-破骨共育体系中对成骨细胞(OB)增殖、OB碱性磷酸酶(ALP)活性、破骨细胞(OC)活性及OB雌激素受体(ER)α及βmRNA表达的影响,从细胞水平阐释其防治骨质疏松症的作用机制。方法:分别选取1 d和5 d SD大鼠分离培养OB和OC,并建立OB-OC共育体系;在共育体系中,用MTT法检测低浓度(0.05、0.1、0.5、1 mg/L)、中浓度(2、5、10 mg/L)和高浓度(20、50和100 mg/L)梓醇干预下的OB增殖率,并以梓醇最佳促OB增殖浓度进行后续实验,实验分为对照组和梓醇组。p NPP法检测各组OB的ALP活性;光镜观察OC骨吸收陷窝数目;重氮盐法检测OC抗酒石酸酸性磷酸酶(TRAP)的活性;RT-PCR方法检测OB ERα及ERβmRNA的表达。结果:在OB-OC共育体系中,0.05~2 mg/L梓醇各组中OB的增殖率显著高于对照组(P0.01),且0.05 mg/L梓醇组促进OB增殖的能力明显高于其它浓度组(P0.01),5~100 mg/L梓醇各组OB的增殖率与对照组比较无显著差异(P0.05)。0.05 mg/L梓醇组的ALP水平高于对照组(P0.05),并在作用48、72和96 h后均对OC骨吸收陷窝数及TRAP有明显抑制作用(P0.01);0.05 mg/L梓醇组OB中ERαmRNA的表达与对照组相比差异无统计学意义(P0.05),而ERβmRNA的表达显著高于对照组(P0.05)。结论:梓醇在共育体系中可提高OB增殖和成骨活性,抑制OC活性并上调OB中ERβmRNA的表达。     

Temporal pattern of stimulation of osteoblast-associated genes during mechanically-induced osteogenesis in vivo: early responses of osteocalcin and type I collagen.

Mechanical loading is an essential environmental factor in skeletal homeostasis, but the response of osteoblast-associated genes to mechanical osteogenic signal is largely unknown. This study uses our recently characterized in vivo osteoinductive model to analyze the sequence of stimulation and the time course of expression of osteoblast-associated genes in mechanically loaded mouse periodontium. Temporal pattern of regulation of osteocalcin (OC), alkaline phosphatase (ALP), and type I collagen (collagen I) was determined during mechanically-induced osteoblast differentiation in vivo, using a mouse tooth movement model earlier shown to induce bone formation and cell-specific regulation of genes in osteoblasts. The expression of target genes was determined after 1, 2, 3, 4, and 6 days of orthodontic movement of the mouse first molar. mRNA levels were measured in the layer of osteoblasts adjacent to the alveolar bone surface, using in situ hybridization and a relative quantitative video image analysis of cell-specific hybridization intensity, with non-osseous mesenchymal periodontal cells as an internal standard. After 24 hours of loading, the level of OC in osteoblasts slightly decreased, followed by a remarkable 4.6-fold cell-specific stimulation between 1 and 2 days of treatment. The high level expression of OC was maintained throughout the treatment with a peak 7-fold stimulation at day 4. The expression of collagen I gene was not significantly affected after 1 day, but it was stimulated 3-fold at day 2, and maintained at a similar level through day 6. The ALP gene, which we previously found to be mechanically stimulated during the first 24 hours, remained enhanced from 1.8- to 2.2-fold throughout the 6 days of treatment. Thus, in an intact alveolar bone compartment, mechanical loading resulted in a defined temporal sequence of induction of osteoblast-associated genes. Stimulation of OC 48 h after the onset of loading (and 24 h prior to deposition of osteoid) temporally coincided with that of collagen I, and was preceded for 24 h by an enhancement of ALP. Identification of OC as a mechanically responsive gene induced in functionally active osteoblasts in this study is consistent with its potential role in limiting the rate of mechanically-induced bone modeling. Furthermore, these results show that temporal progression of mechanically-induced osteoblast phenotype in this in vivo model occurs very rapidly. This suggests that physiologically relevant mechanical osteoinductive signal in vivo is targeting a population of committed osteoblast precursor cells that are capable of rapidly responding by entering a differentiation pathway and initiating an anabolic skeletal adaptation process.     

Cultured Human Periosteal-Derived Cells Have Inducible Adipogenic Activity and Can Also Differentiate Into Osteoblasts in a Perioxisome Proliferator-Activated Receptor-Mediated Fashion

We investigated the adipogenic activity of cultured human periosteal-derived cells and studied perioxisome proliferator-activated receptor (PPAR) ligand-mediated differentiation of cultured human periosteal-derived cells into osteoblasts. Periosteal-derived cells expressed adipogenic markers, including CCAAT/enhancer binding protein α (C/EBP- α), C/EBP-δ, aP2, leptin, LPL, and PPARγ. Lipid vesicles were formed in the cytoplasm of periosteal-derived cells. Thus, periosteal-derived cells have potential adipogenic activity. The PPARα and PPARγ agonists, WY14643 and pioglitazone, respectively, did not modulate alkaline phosphatase (ALP) activity in periosteal-derived cells during induced osteoblastic differentiation, however, the PPARα and PPARγ antagonists, GW6471 and T0070907, respectively, both decreased ALP activity in these cells. WY14643 did not affect, whereas pioglitazone enhanced, alizarin red-positive mineralization and calcium content in the periosteal-derived cells. GW6471 and T0070907 both decreased mineralization and calcium content. By RT-PCR, pioglitazone significantly increased ALP expression in periosteal-derived cells between culture day 3 and 2 weeks. Pioglitazone increased Runx2 expression after 3 days, which declined thereafter, but did not alter osteocalcin expression. Both of GW6471 and T0070907 decreased ALP mRNA expression. These results suggest that pioglitazone enhances osteoblastic differentiation of periosteal-derived cells by increasing Runx2 and ALP mRNA expression, and increasing mineralization. GW6471 and T0070907 inhibit osteoblastic differentiation of the periosteal-derived cells by decreasing ALP expression and mineralization in the periosteal-derived cells.In conclusion, although further study will be needed to clarify the mechanisms of PPAR-regulated osteogenesis, our results suggest that PPARγ agonist stimulates osteoblastic differentiation of cultured human periosteal-derived cells and PPARα and PPARγ antagonists inhibit osteoblastic differentiation in these cells.     

15-deoxy-Delta 12,14-ProstaglandinJ2 regulates dedifferentiation through peroxisome proliferator-activated receptor-gamma-dependent pathway but not COX-2 expression in articular chondrocytes

Peroxisome proliferator-activated receptors-gamma (PPAR-gamma) is critical for phenotype determination at early differentiation stages of mesenchymal cells, whereas its physiological role is unclear. Therefore, we investigated the role of 15-deoxy-Delta(12,14)-prostaglandinJ2 (15d-PGJ2), the natural receptor ligand for PPAR-gamma, on dedifferentiation and inflammatory responses, such as COX-2 expression and PGE2 production, in articular chondrocytes. Our data indicate that the 15d-PGJ2 caused a loss of differentiated chondrocyte phenotype as demonstrated by inhibition of type II collagen and proteoglycan synthesis. 15d-PGJ2 also induced COX-2 expression and PGE2 production. The 15d-PGJ2-induced dedifferentiation effect seems to be dependent on PPAR-gamma activation, as the PPRE luciferase activity increased and PPAR-gamma antagonist, BADGE, abolished type II collagen expression. However, BADGE did not block 15d-PGJ2-induced COX-2 expression. Collectively, our findings suggest that PPAR-gamma-dependent and -independent mechanisms of 15d-PGJ2-induced dedifferentiation and inflammatory responses in articular chondrocytes, respectively. Additionally, these data suggest that targeted modulation of the PPAR-gamma pathway may offer a novel approach for therapeutic inhibition of joint tissue degradation.